This comprises a continuing study in patients with acute cerebrovascular disease, with particular emphasis on the investigation of transient ischemic attacks. The study is designed to define the properties of the transient ischemic attack which allow it to be an accurate predictor of an impending ischemic infarct. The study includes further investigation defining the mechanism of transient focal cerebral ischemia in each individual case in order to describe the frequency and nature of all mechanisms operative in the production of such episodes. Up to the present time approximately fifty such patients have been evaluated with a systematized diagnostic approach. The results are presently being analyzed.